Which of the following numbers is a factor of 80? ${3,5,7,11,14}$
Explanation: By definition, a factor of a number will divide evenly into that number. We can start by dividing $80$ by each of our answer choices. $80 \div 3 = 26\text{ R }2$ $80 \div 5 = 16$ $80 \div 7 = 11\text{ R }3$ $80 \div 11 = 7\text{ R }3$ $80 \div 14 = 5\text{ R }10$ The only answer choice that divides into $80$ with no remainder is $5$ $ 16$ $5$ $80$ We can check our answer by looking at the prime factorization of both numbers. Notice that the prime factors of $5$ are contained within the prime factors of $80$ $80 = 2\times2\times2\times2\times5 5 = 5$ Therefore the only factor of $80$ out of our choices is $5$. We can say that $80$ is divisible by $5$.